1. Field of the Invention
The present invention relates to a flash-fixing color toner for use in the development of an electrostatic latent image in electrophotography and the like and a process for producing the same. More particularly, the present invention is concerned with a flash-fixing color toner which comprises as an indispensable ingredient a near-infrared light absorber composed mainly of an aminium salt compound which allows the triboelectric property of a toner to be regulated, and a process for producing the same.
2. Description of the Related Art
Electrophotography known in the art includes a system described in U.S. Pat. No. 2297691 and the like. In this system, a photoconductor (a photoconductive drum or the like) is generally used, an even electrostatic charge is provided on the surface of the photoconductor by corona discharge or the like, and an optical image is applied onto the photoconductor by various means to form an electrostatic latent image that is then developed with a fine powder called a "toner".
If necessary, the toner image is transferred onto a recording medium, such as paper. The toner image is then melted by means of pressing, heating, solvent vapor, light or the like to fix the toner image to the recording medium, thereby providing a print.
Particles formed by pulverizing a dispersion comprising a binder resin comprised of a naturally occurring or synthetic polymeric material and, dispersed in the binder resin, a coloring material and optionally additives, such as a charge control agent, to a size of about 1 to 30 .mu.m have hitherto been used as the toner for developing the electrostatic latent image.
In an electrophotographic two-component development process, the above-described toner is usually mixed with a carrying material (a carrier) including a ferromagnetic material, such as an iron powder, or a glass bead, before use in the development of the electrostatic latent image. In the case of a magnetic brush development process using as the carrier ferromagnetic particles, such as an iron powder or ferrite, the development is effected by mixing and stirring a developer comprising a toner and a carrier in a developing unit to effect triboelectrification, holding the triboelectrified toner with a magnetic roll in the developing unit to form a magnetic brush that is then transferred to a latent image portion on a photoconductor where charged toner particles alone are adhered to the latent image by electric attraction.
In this case, a polymer resin generally called an "oligomer", having a low molecular weight to exhibit a low melting viscosity, is extensively used as the binder resin, because the binder resin constituting the toner should be rapidly fused and exhibit a good fixation in the stage of the fixing of the toner to a recording medium.
In the above-described fixation, the toner on recording paper is fused by means of pressing, heating, exposing solvent vapor, irradiating light, etc. and then anchored to the recording paper. Among these fixing methods, the photo-fixing method has attracted attention because it has the following features.
(1) No deterioration of the resolution of the image in the stage of the fixing occurs by virtue of non-contact fixation. PA1 (2) Quick start is possible because there is no need for waiting time after turning on the power. PA1 (3) Even though a system failure may give rise to a recording paper jam within a fixing unit, there is no danger of the recording paper being ignited. PA1 (4) The fixing can be successfully effected independently of the material and thickness of the recording paper even when use is made of glued paper (tack paper), preprint paper and various kinds of paper different from each other in the thickness. PA1 (i) means where a mixture of a plurality of resins is used as the binder resin and the infrared light absorber is selectively dispersed or dissolved in a particular resin constituting a part of the plurality of resins, PA1 (ii) means where a positive charge control agent and/or a binder resin containing a positive charge control agent are coated on or deposited in a fine particle form on the outer periphery of a toner comprising an infrared light absorber, a coloring material and a binder resin, PA1 (iii) means where an infrared light absorber and/or a binder resin containing an infrared light absorber are coated on or deposited in a fine particle form on the outer periphery of a toner comprising a positive charge control agent, a coloring material and a binder resin, PA1 (iv) means where a mixture of an amine-functional-group-containing resin, which contains a secondary amine and/or a tertiary amine and/or a quaternary amine and/or a quaternary ammonium salt, and a resin containing an acidic functional group is used as the binder resin to block the amine-functional-group-containing resin and/or the quaternary ammonium salt with the resin containing an acidic functional group, PA1 (v) means where at least one member selected from the group consisting of a thermoplastic resin having an amide group and/or a pendant group of a nitrogen-containing ring, an amide compound, a polyamide resin, an amine-modified polyester resin, a urethane-modified polyester resin and an amine-modified epoxy resin crosslinked with a diamine is used as the binder resin, PA1 (vi) means where a quaternary ammonium salt represented by the following general formula (3) is used as the positive charge control agent: ##STR5## wherein R.sup.1 to R.sup.4 each represent an arbitrary alkyl group, a phenyl group or a derivative thereof and X.sup.- represents the same anion as that defined in the general formulae (1) and (2), PA1 (vii) means where the infrared light absorber is composed of either a compound represented by the general formula (1) in combination with a compound represented by the general formula (2) with an anion X.sup.- common to both the compounds or at least two compounds represented by the general formula (1), PA1 (viii) means where at least one of compounds represented by the general formulae (4) to (8) is additionally used as a component of the infrared light absorber: ##STR6## wherein ##STR7## represents an aromatic ring having a skeleton represented by ##STR8## x represents hydrogen, a halogen, an alkyl or a halogenated alkyl, S represents sulfur, M represents nickel, cobalt, platinum or palladium and A represents a quaternary ammonium salt, ##STR9## wherein ##STR10## represents an aromatic ring having a skeleton represented by ##STR11## X represents hydrogen, a halogen, an alkyl or a halogenated alkyl, S represents sulfur, O represents oxygen, M represents nickel, cobalt, platinum or palladium and A represents a quaternary ammonium salt, ##STR12## wherein ##STR13## represents an aromatic ring having a skeleton represented by ##STR14## x represents hydrogen, a halogen, an alkyl or a halogenated alkyl, R represents hydrogen, an alkyl or a halogenated alkyl, N represents nitrogen, M represents nickel, cobalt, platinum or palladium and A represents a quaternary ammonium salt, ##STR15## wherein R represents hydrogen, an alkyl or a halogenated alkyl having 1 to 4 carbon atoms, O represents oxygen, S represents sulfur and n is a positive integer, and ##STR16## wherein ##STR17## represents an aromatic ring having a skeleton represented by ##STR18## X represents hydrogen, a halogen, an alkyl or a halogenated alkyl, N represents nitrogen, M represents a divalent metal atom, a tri- or tetravalent substituted metal atom or two hydrogen atoms.
The current most con, non photo-fixing method is a flash fixing method using a xenon flash lamp as a light source.
In a photo-fixing method that uses a light source having a high luminous intensity at wavelengths in an infrared region, such as the xenon flash fixing method, the addition of an infrared light absorber, such as an aminium salt compound, in a toner has been proposed in Japanese Unexamined Patent (Kokai) No. 61-132959 for the purpose of improving the light absorption capability of the toner and expanding the range of utilization of the photo-fixing method having the above-described advantages.
Many of compounds having a high infrared absorption capability have hues ranging from brown to black. The aminium salt compounds, however, exhibit an excellent infrared absorption capability and, at the same time, have a light color tone in a visible light region, so that the toner, as such, is less likely to have an influence on the color tone of the toner, which renders these compounds very useful for making up for the light absorption capability of the color toner.
Since, however, the aminium salt compounds are substances having a salt structure having a counter ion as represented by the following formulae: ##STR1## wherein X.sup.- is an arbitrary anion with an arbitrary valency; and ##STR2## wherein X.sup.- is an arbitrary anion with an arbitrary valency, when a high polar site (for example, a substance which have a tertiary amine group, such as dimethylaminoethyl methacrylate) and a high reactive ionic compound (for example, a quaternary ammonium salt) are present in the toner, the counter ions of the aminium salt compounds are extracted by the polar group or give rise to a counter ion exchange reaction with the ionic compound.
This causes a structural change of the aminium salt compound, which results in a shift in the light absorption band of the aminium salt compound and, in extreme cases, a complete loss of the capability of absorbing light having wavelengths in a flash light region.
On the other hand, the quaternary ammonium salt has an excellent charge control capability as a colorless positive charge control agent and is commonly used in color toners. The addition of an amine compound other than the quaternary ammonium salt to the toner, the introduction of an amine functional group into the binder resin, or other means, is used as a method for imparting a positive chargeability to the toner without use of the quaternary ammonium salt. As described above, however, the amine compound too has a high possibility of causing a structural change to the aminium salt compound.
For the reasons set out above, the aminium salt compound for improving the light absorption capability cannot be used in combination with the amine compound for imparting a charge control capability (hereinafter referred to as a "charge control agent"), such as a quaternary ammonium salt, and there is a problem that a positive charge color toner having an excellent light absorption capability and a good photo-fixability is poor in the chargeability, while the positive charge color toner having an excellent chargeability is poor in photo-fixability.
The present invention has been made in view of the above-described problems of the prior art, and an object of the present invention is to provide a flash fixing toner that enables the structural change of the aminium salt compound to be minimized while the aminium salt compound and a charge control agent coexist in a toner, thereby attaining a combination of an excellent flash fixability with an excellent chargeability, and a process for producing the same.